1. Field of the Invention
The present invention relates to a silicon-containing polymer and a chemically amplified bilayer resist composition. More particularly, the present invention relates to a chemically amplified bilayer resist composition for use in a broad range of microlithography, including ArF lithography, electron beam lithography, etc., which performs well in terms of adhesion to Si substrates, exposure and development, and dry etch resistance.
2. Description of the Prior Art
In the electronics industry, the high degree of integration in circuits requires fine patterns, making the fabrication process of semiconductor devices highly complicated. Accordingly, novel resists have been in great demand for use in optical lithography.
Conventional resist materials are incapable for ArF lithography because of their poor transparency at 193 nm wavelength. As the capacity of semiconductor devices exceed 4 G bit, it is necessary to develop a new resist material for ArF excimer laser lithography with high optical transparency at the exposure wavelength.
For example, 4G bit or larger scaled semiconductor devices can be achieved by the microlithography using ArF eximer laser as a light source, whose wavelength (193 nm) demands novel resists different from those used for the microlithography using longer wavelengths.
ArF resists may be classified into two types by their fabrication processes: single layer resist (SLR) and bi-layer resist (BLR). The SLR allows the formation of resist patterns to be achieved easily; however, it cannot guarantee sufficient dry etch resistance on the resist patterns formed therefrom. Additionally, when its aspect ratios are increased, the SLR pattern formations are apt to collapse, which makes it difficult to establish the patterns. By contrast, when the BLR, which contains silicon, is used to form resist patterns, intricate processes are required.
However, since the silicon atoms in the resists crystallize into glass upon dry etching with O2 plasma, to form a hard layer at the surface of the resist, the BLR allows for the easy formation of resist patterns even at large aspect ratios.
Serving as an important factor in preparing the BLR, the content of silicon in the BLR is required to amount to be equal to or greater than 10% by weight in order to secure sufficient aspect ratios. Silicon-containing polymers, available as BLR for use in ArF excimer laser lithography, are described in J. Photopolymer Science and Technology, No. 4, Vol.8, p.615 1995, Akiko Kotachi, et al., xe2x80x9cSi-Containing Positive Resist for ArF Excimer Laser Lithography.xe2x80x9d
The polymers disclosed in the literature contain silicon in an amount of 8% by weight which is too small to guarantee sufficient aspect ratios. Additionally, these polymers adhere poorly in terms of adhesion to substrates that the resist films prepared therefrom are apt to separate from their substrates.
U.S. patent application Ser. No. 08/942,249, filed September 1999 by the present inventors, discloses a BLR which is prepared using a 1,3-bis(trimethylsilyl)isopropyl methacrylate (BPMA) as a silicon-containing monomer. With an acid moiety having an unstable group, the BPMA monomer can be very useful for the preparation of BLR. Resists using the monomer disclosed by the present inventors in the following publication: e.g., J. Photopolymer Science and Technology, No. 4, Vol. 10, 1997, Kang, Y. J., Lee, H. et al.; Chemically Amplified Silicon Containing Resist for ArF Excimer Laser Lithography, p.585; Mol. Cryst. Liq. Cryst., 1999, 327, Kim, Y. D., Lee, H, et al.; New Bilayer Positive Photoresists for 193 nm Photolithography, p.279; Korean Patent. Publication No. 10-1999-230417, issued Dec. 15, 1999 to the present inventors.
Although easily formable form into patterns as fine as 1 xcexcm or less, the resists disclosed in the above literature cannot be used in practice because they are not developed at the required solution""s concentration in microlithography processes (e.g. 2.38 wt % TMAH).
With the above problems in mind, it is an object of the present invention to provide copolymers of novel structures, which show good enough transmittance at 193 nm wavelength in using ArF excimer laser lithography, contain a silicon content sufficient for use in BLR, and are capable of being developed in 2.38 wt % TMAH (tetramthyl ammonium hydroxide) solution.
It is another object of the present invention to provide polymers which are improved in etch resistance and perform very well in terms of adhesion to substrates.
It is a further object of the present invention to provide chemically amplified resist compositions containing the copolymers.